CVE-2026-116685 Model Context Protocol Python SDK: HTTP client transports followed cross-origin redirects carrying custom headers and bodies
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-116685?
CVE-2026-116685 is a medium-severity vulnerability in modelcontextprotocol python-sdk, published on 27 Oct 2026.
Official description
The Model Context Protocol Python SDK is the official Python SDK for Model Context Protocol servers and clients. From 1.8.0 until 1.30.0 and 2.2.0, streamable_http_client, streamablehttp_client, sse_client, ClientSessionGroup, OAuth, and create_mcp_http_client client paths enable follow_redirects and follow redirects to a different origin, forwarding caller-supplied custom credential headers and, for 307 or 308 responses, the request body. An attacker who can influence a trusted endpoint's redirect destination can receive that material. This issue is fixed in versions 1.30.0 and 2.2.0.
Weakness: CWE-200
Which versions are affected by CVE-2026-116685?
4 open source packages ship an affected version, including mcp.
| Package | Affected | Fixed in |
|---|---|---|
mcp PyPI | From 1.8.0 | 1.30.0 |
mcp PyPI | From 1.8.0 | 1.30.0 |
mcp PyPI | From 2.0.0 | 2.2.0 |
mcp PyPI | From 2.0.0 | 2.2.0 |
How do I fix CVE-2026-116685?
Upgrade mcp to a fixed version for your release line: 1.30.0 or 2.2.0.
Is CVE-2026-116685 being exploited?
There is no known exploitation of CVE-2026-116685 in the wild and no public exploit code.
Sources
Also known as GHSA-5h93-6whr-6q8j.